There are two methods that I use to bring a cold
gun into a warm environment. If the gun is in a
case that is also cold, I bring it into my unheated
and enclosed porch. It is usually just above
freezing there. After it's been the a half day or
so, I bring it into the house and don't remove it
from the case for a few hours more.
The other method, is to bring it inside and get it
next to a heater, hot enough so that the moisture
evaporates. The the gun gets a good wipe down
with gun oil or CLP.